(1) Field of the Invention
The invention relates to field emission flat panel displays, and more particularly to structures and methods of manufacturing field emission displays that provide brightness enhancements for improved end-user viewing.
(2) Description of the Related Art
In display technology, there is an increasing demand for flat, thin, lightweight displays to replace the traditional cathode ray tube (CRT) device. One of several technologies that provide this capability is field emission displays (FED). An array of very small, conical emitters is manufactured, typically on a semiconductor substrate, and can be addressed via a matrix of row and column electrodes. One set of these electrodes runs under and is electrically connected to the emitters and is usually referred to as the cathode. The other set of electrodes is formed above and perpendicular to the cathode lines and has an aperture surrounding the tip of each emitter, and is usually referred to as the gate. When a positive voltage differential is applied between the gate and cathode, a strong electric field is created at the emitter tips, and electron emission occurs. A third conductive surface, the anode, at a different voltage, attracts the emitted electrons. Cathodoluminescent material formed over the anode emits light when excited by the emitted electrons, thus providing the display element. The anode is typically mounted in close proximity to the cathode/gate/emitter structure.
FIG. 1 is a cross-sectional view of a typical field emission display of the related art. Row electrodes 12, or cathode, are formed on a substrate 10, and have emitter tips 14 mounted thereon. The emitters are separated by insulating layer 16. Column electrodes 18, the gate, with openings for the emitter tips, are formed over the insulating layer 16 and perpendicular to the row electrodes. When electrons 19 are emitted, they are attracted to conductive anode 22 and upon striking phosphor dot 20, light 26 is emitted, which can be viewed through the transparent faceplate 24. However, light 26 that is emitted in the direction of a viewer of the display, who would be looking through glass plate 24, must travel through the phosphor 20, the anode 22 and the glass 24. The luminous efficiency of the display is reduced primarily due to absorption by the phosphor.
Workers in the art are aware of this problem and have attempted to resolve it, with one approach disclosed in U.S. Pat. No. 5,216,324 (Curtin), in which the display image is viewed through the back plate, either by forming the conductive and insulating layers on the back plate of a transparent material, or making the conductive lines very thin, both of which increase the amount of light that can be transmitted to the viewer.
U.S. Pat. No. 4,908,539 to Meyer discloses a change in the location of the anode/phosphor 30, from the faceplate to the top of the column electrode 18, as shown in FIG. 2. This eliminates the light loss in the FIG. 1 structure that occurs as the emitted light passes through the phosphor. However, this method suffers from the problem of requiring a low-voltage phosphor, since otherwise the insulator may not be able to sustain the high voltage on the phosphor layer.
U.S. Pat. No. 4,857,799 (Spindt) discloses the use of phosphor strips and the fact that the close cathode-phosphor spacing enables the gate structure to act as a reflective surface to increase the effective brightness. However, this arrangement suffers from degraded contrast at each pixel due to the lack of black material in the spaces between the phosphor strips.